Japanese Laid-Open Patent Publication No. 10-45290 discloses an automatic web splicing apparatus for splicing a web with another web while maintaining a constant tension on the web. With the conventional apparatus, the web velocity is detected by a line pulse generator on the output side of the automatic splicing apparatus to calculate the diameter of a roll of web based on the web velocity, or the like, and the braking force is controlled based on the diameter of the roll, or the like, thereby maintaining a constant torque. However, maintaining a constant line velocity on the output side of the automatic splicing apparatus is not taken into consideration.